Jack Leonard reports in the LA Times:

Opening a new frontier for solving cold cases, California prosecutors are hunting for DNA from killers, rapists and other prison inmates who died before authorities obtained their genetic profiles.

Prosecutors from Sacramento, Los Angeles and Orange counties are sifting through old court exhibits and examining long-since forgotten crime-scene evidence in search of blood, saliva and other material that can be tested for DNA. Once obtained, the DNA is compared with the genetic profiles from unsolved cases that have DNA from unidentified perpetrators.

Of course, there is no case to prosecute where the perp is dead.  However, knowing that the case is solved and the perp is indeed dead is a great service to the victim or the victim's family.

The ACLU isn't quite as exercised about the privacy rights of dead people.  Even so, they are warning about getting samples from exhumations or medical samples.